X-ray crystal structure determinations will be carried out on biologically significant materials including certain forms of cholesterol, at least one protein, and a crystalline virus. The work will primarily rely on computer-based structure solving and refinement methods. These include Patterson search methods and Gauss-Seidel least squares refinement as well as techniques which utilize the known non-crystallographic symmetry present in an otherwise unknown structure. BIBLIOGRAPHIC REFERENCE: J.C. Hanson and C.E. Nordman, The Crystal and Molecular Structure of Corannulene, C20 H10. Acta Cryst. B32, 1147 (1976).